These animals are rather robust. Marked dorsal and ventral ridges are present on the peduncle. The melon has a distinct apex, blending indistinctly with the snout. There are some regional variations in size, but on average adult hump-backed dolphins are 210-220 cm long (range: 180-279 cm) (Ross et al, 1994). They weigh 80-100 kg. They have 29-38 pairs of peg-like teeth in each jaw (26-31 for S. teuszii) (Evans, 1987).

Hump-backed dolphins are slow swimmers (4.8 km/hr) and surface briefly at long intervals (40-60 seconds). Their characteristic high roll when surfacing probably gave them their common name.

Distribution

The Indo-Pacific hump-backed dolphin can be found in the coastal waters of the Indian Ocean and the Western Pacific Ocean, from the northern East China Sea to New South Wales, Australia. This is a distinctly tropical species, associated with warm waters (15-36°C). They usually live in shallow waters (less than 20 m deep). In Moreton Bay, Australia, all sightings of this species occur in waters of 10 m deep or less and within 6 km of the coast.

Population dynamics and life history

Neonate calves are about 1 m in length. There appears to be no seasonality in reproduction. Very little is known about maturation and mortality in this species.

Population status

There is very little data on the abundance of the species anywhere in its range.

Exploitation

In the Arabian Sea, Red Sea and Persian Gulf, small numbers have been taken for their meat. They do occassionally get entangled in shark nets off South Africa (about 8/year) (Klinowska, 1991). Some animals have been captured for live display. One animal, a female captured in 1966, is still on display at Sea World, Gold Coast, Australia. The dolphins of Imraguens de N’memghar, Mauretania, co-operate with local fishermen in their fisheries for mullet. This co-operation seems to benifit both humans and dolphins (Klinowska, 1991). As a result, the local fishermen are very protective of “their” dolphins, although they will utilize stranded or accidently killed dolphins.

Feeding

The hump-backed dolphin feeds mainly on fish species. The species taken depend on the area, but include clupeids (herring family) and mullet, as well as small reef fishes.

A sociable hump-backed dolphin

In Tin Can Bay, Queensland, Australia, a female hump-backed dolphin appears daily to interact with bathers. In 1996, she had a calf and took the calf with her on her visits to the Bay. Her visits probably started when people offered her fish. Recently feeding her has been discontinued and is actively discouraged, but she continues to visit the Bay.